Much concern is being expressed regarding the high nitrogen oxides levels of exhaust gases from lignite-fired and coal-fired electric power plants and industrial boilers, particularly those having very large fireboxes to accommodate high moisture-content coals and lignites, which are inherently low in fuel value. The typical fuels of concern are the lignites of North Dakota and Texas and the low-sulphur coals of the Powder River Basin in Wyoming. The large fireboxes required to provide sufficient retention time for the relatively complete combustion of these types of coaliferous fuels causes the formation of very high levels of nitrogen oxides in the exhaust gases. These are some of the lowest sulphur-level coaliferous fuels in the nation, and for that reason are most desirable for use as boiler fuels, except for the high nitrogen oxides emissions produced.
The problem arises from the inherently poor combustion characteristics of many coals, the long combustion time intervals required, and the great amounts of excess combustion air required to complete combustion. New means effectively reduce the nitrogen oxides emissions from the types of boiler plants described hereinabove and from other boiler plants burning coals, lignites or anthracites which are difficult to burn.
New boiler plants can be specifically designed for the greatly improved fuels described hereinafter. Preparing the fuels at the mine site and shipping them in sealed containment by truck, rail, barge or ship can greatly reduce the cost per unit of heating value for shipping coals which otherwise would have to be shipped at high moisture levels.